An electrophotographic light-sensitive medium is usually prepared using an electrically-conductive medium. Known electrically-conductive supports include a metallic plate, an insulative resin film with a metal or metal oxide thin film provided on the surface thereof by vacuum-deposition or sputtering, a paper made electrically-conductive using a polymeric electrolyte (e.g., a quaternary ammonium salt), and a support prepared by providing an electrically-conductive layer comprising a binder and electrically-conductive metal oxide particles dispersed therein on paper or a like material (support of this type is described in Japanese Patent Application (OPI) Nos. 25140/76 and 113224/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")). A method of providing a transparent electrically-conductive layer on a transparent resinous film wherein cuprous iodide is used is described in U.S. Pat. No. 3,428,451 and Japanese Patent Publication No. 34499/71. Furthermore, a method of providing a thin film of tin dioxide or indium oxide on glass or a like material is known.
However, problems described below arise in preparing a transparent electrophotographic light-sensitive medium utilizing the foregoing known methods. The term "transparency" as used herein means that the transmittance of light having a wavelength range including visible light is about 50% or more, and the light-scattering efficiency about 50% or less.
A metal-deposited film lowers transmittance and increases production costs. A metal oxide thin film further increases production costs, although it increases the transmittance. When a polymeric electrolyte is used, the resulting electrically-conductive layer has high dependency on humidity. When an electrically-conductive layer is provided on a transparent resinous film and interposed between the film support and a light-sensitive layer, the electrically-conductive layer often becomes highly resistant since the electrically-conductive layer is prevented from absorbing moisture.
The above-cited references disclosing use of electrically-conductive metal oxides indicate that the electrically-conductive layer contains a large amount of oxide particles in preferred embodiments. The amount of the binder is about 30 parts by weight or less per 100 parts by weight of particles. Therefore, it is difficult to form a transparent electrically-conductive layer.
When cuprous iodide is used, a transparent electrophotographic light-sensitive layer can be prepared. However, the layer has a pale yellow color and thus the quality of an image is disadvantageously deteriorated. In general, it is not desirable for the image background area to be colored yellow or red. However, it is acceptable if the background area is bluish.
In some cases, metal oxide thin film formed by vacuum-deposition or sputtering has inferior adhesion to the electrophotographic light-sensitive medium on which it is provided, while the method provides excellent transparency and electrical conductivity.